﻿using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp2
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("hello world!");


            double a = 3.14;
            Console.WriteLine("请输入圆的半径：");
            double b = double.Parse(Console.ReadLine());
            Console.WriteLine(a*b*b );
            Console.ReadKey();

        }
    }
}
